The mother of one of the lead actors in St Kentigern College's ill-fated production of Sweeney Todd says it's still a mystery how two of the characters received cuts to their neck from a prop razor.

Remaining shows of the Auckland private school's production were cancelled after two 16-year-old cast members were hospitalised on Wednesday.

A prop razor, reportedly blunted and wrapped in protective layers, caused the injuries in the play that centres around an English barber and serial killer who slits his clients' throats before they are made into meat pies by struggling pie shop owner, Mrs Lovett.

Pam Nobbs, whose daughter Olivia played Johanna -- the daughter of Sweeney Todd -- said the incident was just a "terrible accident".


"All we can say is it was just a terrible accident. It is still a mystery to everybody [what happened], nobody knows and they are still trying to figure out what went wrong.

"It's very odd -- they practised so many times and it all went fine, maybe [the blade] just wore through, I don't know."

She said her daughter, like her family watching in the audience, did not know anything had gone wrong until after the show.

"Everybody was so busy with the show that they didn't quite realise what was happening because it had never happened in all the practices.

"She didn't gather that it was major, she thought it was a little thing that went wrong and the boys would be back to school in no time."

The boys were released from hospital on Thursday.

"I understand the boys are recovering well, to be honest I think the media has made it sound worse than it actually was.

"Obviously anybody being cut is a serious concern and any parent would be worried about that, but I think it's been blown out of proportion to reality -- accidents happen, it is just very unfortunate that it has happened."


Mrs Nobbs said all the students and teachers involved poured their energy into the production and were disappointed it had been cancelled.

"They are very, very disappointed. They put weeks and weeks into it, they practised so many times and I can't speak highly enough of the school or the teachers for the effort they had put it."

She was not concerned that the school has used real razors and was confident with their safety procedures and risk assessments protocols, she said.

"The students have all been incredibly well supported by the school. This is Olivia's 13th year at the school and we have never had any complaints or issues with anything."

The high profile incident -- that has been published by media organisations worldwide -- is being investigated by the school, police and WorkSafe New Zealand.

School headmaster Steve Cole said he was not concerned about possible consequences for the school under new health and safety laws which came into force on Monday.

"We're very confident in our health and safety procedures.

"My concern is for the two boys and their families."